The present invention relates to a cover assembly, particularly a cover assembly for an internal combustion engine, with the cover assembly including a flange, openings for the passage of fastening screws, and sound insulating elastomer bodies provided in the openings.
Due to its complex structure and mode of operation, an internal combustion engine generates noise, some of which is caused by components that are connected with the engine but are not power transmitting components. Examples include valve covers and oil pans. In an attempt to reduce noise it has been found to be an effective measure to fasten these components so that they are insulated against structure-borne sound.
DE-OS (German Unexamined Published Patent Application) 2,723,459 discloses an internal combustion engine in which an oil pan is connected to the crankcase in a manner insulated against structure-borne sound- The fastening screws for the oil pan are embedded in elastomer bodies having guide rings which extend into the openings for the fastening screws. In order to protect the elastomer bodies against excess stresses, fixed abutments are provided at the oil pan and at the housing of the internal combustion engine.
One drawback of this structure is that during installation of the oil pan, the biasing force of the seal and of the elastomer bodies is set by way of the fastening screws, in that the screws are screwed into the housing to the end of their threads. Since the rigidity of the individual elastomer bodies may differ it is not possible to set them all optimally, particularly if there are a plurality of elastomer bodies distributed over the periphery of the housing but the threaded portions of the screws are always of the same length. Moreover, the individual elastomer bodies must all be produced as separate components in a vulcanization mold and must also be installed individually. If there are vertical vibrations, the abutments may hit against one another, thus enabling the transmission of structure-borne sound.
In a cylinder head cover for an internal combustion engine as disclosed in German Patent 3,639,218 (corresponding to U.S. Pat. No. 4,819,953), elastomer bodies are pressed into the openings for the fastening screws in order to provide for insulation against structure-borne sound. In this arrangement as well, the elastomer bodies are manufactured separately and pressed into the openings in an additional process step. The thread-free section of the fastening screw serves as a path-limiting member for setting the biasing force of the seal.